This component calculates the wind pressures for each structural element and applies the load in different directions, in accordance with AASHTO 3.8.1.2. The nodal loads are then determined by converting the wind pressure values according to their respective tributary areas, for different angles of attack. There are nine cases (-60, -45, -30, -15, 0, 15, 30, 45, and 60) computed for the right-to-left wind direction and another nine cases for the left-to-right wind direction, totaling 18 cases. Envelopes for these 18 cases are automatically generated separately for the Strength III, Strength V, Service I, and Service IV limit states. For each angle of attack, the transverse and longitudinal skew coefficients, reported in the girders column below, are used. Additionally, this component calculates the center of gravity of the girder, deck, and barrier, and applies both forces and moments.
Stage: Choose the stage at which to apply the wind load. The wind load analysis results cannot be visualized within this stage after the analysis. OpenBrIM generates sub-stages automatically and assign selected stage as a prior stage. Therefore, the wind load analysis results will be presented in sub-stages, as shown in the screenshot below.
Structural Objects and Pressure Parameters: This parameter will be enabled if there is no variation in span height.
Applied Elements: Typically, exterior girders, barriers, deck, pier caps and end bents are chosen as the elements to which the wind load is applied.
Wind Direction: Choose the right-to-left direction for barriers or exterior girders located on the right when looking up-station from the alignment. In contrast, select the left-to-right direction for left barriers and exterior girders. For the deck and substructure element, select 'Both Directions' as the wind direction.
Structural Height From Ground Line: According to AASHTO 3.8.1.2.1, the Structure Height, Z parameter is utilized in the computation of Kz - elevation coefficient.
Gust Effect Factor: Gust effect factor determined using a structure specific study or as specified in AASHTO Table 3.8.1.2.1-1 for Strength III and Service IV load combinations and 1.0 for other load combinations. The gust effect factor may vary for different state specifications.
Drag Coefficient: Drag coefficient determined using a structure specific study or as specified in Table 3.8.1.2.1-2. The drag coefficient may vary for different state specifications.
Design Wind Speed: The user inputs the design wind speed for the strength 3 limit state, while the wind speeds for other limit states are calculated using the AASHTO table 3.8.1.1.2-1 shown below.
Surface Roughness[B/C/D]: As stated in AASTO 3.8.1.1.4—Ground Surface Roughness Categories
Ground Surface Roughness B: Urban and suburban areas, wooded areas, or other terrain with numerous closely spaced obstructions having the size of single-family dwellings or larger;
Ground Surface Roughness C: Open terrain with scattered obstructions having heights generally less than 33.0 ft, including flat open country and grasslands; and
Ground Surface Roughness D: Flat, unobstructed areas and water surfaces; this category includes smooth mud flats, salt flats, and unbroken ice.
Span Height Variation
Span Height Variation[Yes/No]: The computed pressure values are a function of the structural heights, as specified in AASHTO 3.8.1.2, which states that "In the case of a long multi-span bridge with a significant variation in the ground surface elevation beneath the bridge, such as a bridge crossing a valley, the structure height, Z, may vary from span to span. For each span, the structure height, Z, can be taken as the largest value in the span." If the user wishes to enter different structural heights for various spans, they should select "yes" for this parameter. In most bridges, it is not necessary to enter different structural heights for various spans, so selecting "yes" for this parameter is not required.
Substructure Objects and Pressure Parameters: This parameter will be activated if there is variation in span height and it is selected as "Yes". All substructure objects should be chosen and entered as described above in the "Structural Objects and Pressure Parameters" section.
Applied Elements
Wind Direction
Structural Height From Ground Line
Gust Effect Factor
Drag Coefficient
Superstructure Objects and Pressure Parameters: This parameter will be activated if there is variation in span height and it is selected as "Yes". All substructure objects should be chosen and entered as described above in the "Structural Objects and Pressure Parameters" section.
Span Number: The span number is the sole additional parameter that allows you to modify the structural height for each span.
Applied Elements
Wind Direction
Structural Height From Ground Line
Gust Effect Factor
Drag Coefficient
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